Medications and Drugs
Medical and Pharmacy Editor: Jay Marks, M.D.
GENERIC NAME: tadalafil
BRAND NAME: Cialis
DRUG CLASS AND MECHANISM:
Tadalafil is an oral drug that is used for treating impotence
(the inability to attain or maintain a penile erection). It is in a
class of drugs called phosphodiesterase inhibitors that also includes sildenafil
(Viagra) and vardenafil (Levitra).
Erection of the penis is caused by the filling of the penis with blood.
Filling occurs because the blood vessels that bring blood to the penis increase
in size and deliver more blood to the penis, and, at the same time, the blood
vessels that take blood away from the penis decrease in size and remove less
blood from the penis.
Sexual stimulation that leads to an erection causes the production and
release of nitric oxide in the penis. The nitric oxide causes an enzyme,
guanylate cyclase, to produce cyclic guanosine monophosphate (cGMP). It is the
cGMP that is primarily responsible for increasing and decreasing the size of the
blood vessels carrying blood to and from the penis, respectively, and causing
the erection. When the cGMP is destroyed by another enzyme, phosphodiesterase-5,
the blood vessels return to their normal size, blood leaves the penis, and the
erection ends. Tadalafil prevents phosphodiesterase-5 from destroying cGMP so
that cGMP stays around longer. The persistence of cGMP leads to a more prolonged
engorgement of the penis with blood.
Tadalafil was approved by the FDA in November, 2003.
PRESCRIPTION: Yes.
GENERIC AVAILABLE: No.
PREPARATIONS: Tablets: 5, 10, and 20 mg.
STORAGE: Store at room temperature between 15-30°C (59-86°F).
PRESCRIBED FOR: Tadalafil is used for the treatment of impotence.
DOSING: For most individuals, the recommended starting dose of tadalafil is
10 mg per day taken before sexual activity. Depending on the adequacy of the
response or side effects, the dose may be increased to 20 mg or decreased to 5
mg a day. The effect of tadalafil may last up to 36 hours. Individuals who are
taking medications that increase the blood levels of tadalafil should not exceed
a total dose of 10 mg in 72 hours (See drug interactions). Tadalafil may be
taken with or without food since food does not affect its absorption from the
intestine.
DRUG INTERACTIONS: The breakdown and elimination of tadalafil from the body
may be decreased by erythromycin, ketoconazole (Nizoral), itraconazole
(Sporanox), indinavir (Crixivan) and ritonavir (Norvir). Therefore, these drugs
may increase the levels of tadalafil in the blood. If these drugs are being used
at the same time as tadalafil, the dose of tadalafil should be reduced in order
to avoid side effects from high levels of tadalafil.
Tadalafil exaggerates the increases in heart rate and lowering of blood
pressure caused by nitrates, e.g. nitroglycerin, isosorbide dinitrate (Isordil),
isosorbide mononitrate (Imdur, Ismo, Monoket), nitroglycerin (Nitro-Dur,
Transderm-Nitro) that are used primarily for treating heart pain (angina). In
patients who take nitrates for angina, tadalafil could cause heart pain or
possibly even a heart attack by exaggerating the increase in heart rate and the
lowering of blood pressure. Therefore, tadalafil should not be used with
nitrates. Tadalafil also exaggerates the blood pressure lowering effects of some
alpha-blocking drugs e.g., terazosin (Hytrin) that primarily are used for
treating high blood pressure or enlargement of the prostate. Individuals who
take these alpha-blockers should be on a stable dose of the alpha-blocker before
tadalafil is started. In such situations, tadalafil should be started at the
lowest dose. If the patient is already taking tadalafil, the alpha-blocker
should be started at the lowest dose. Tadalafil and alcohol both lower blood
pressure. Therefore, combining tadalafil with alcohol may cause excessive drops
in blood pressure and cause dizziness, headaches and increased heart rate.
PREGNANCY: Tadalafil is not approved for use in women.
NURSING MOTHERS: Tadalafil has not been evaluated in women who are breastfeeding.
SIDE EFFECTS: The most common side effects of tadalafil are facial flushing
(reddening), headaches, stomach upset, diarrhea, flu-like symptoms and nausea.
Tadalafil also may cause low blood pressure, blurred vision and changes in color
vision, and abnormal ejaculation. Tadalafil has been associated with prolonged
erections or priapism (painful erections lasting more than 6 hours). Patients
should seek immediate medical help if they experience an erection lasting more
than 4 hours. Use of tadalafil, most often in patients with pre-existing heart
disease, has been associated with chest pain, heart attacks, death, strokes,
palpitations and
increased heart rate; however, it is not clear whether these side effects are
due to tadalafil, concurrent use of nitrates, or the sexual activity itself.
Rare cases of sudden loss of hearing have been reported with phosphodiesterase
inhibitors such as tadalafil, sometimes associated with ringing in the ears
and dizziness. If changes in hearing occur, patients should stop their tadalafil and seek immediate
medical attention.
Reference: FDA Prescribing Information
Last Editorial Review: 10/19/2007
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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